@niodari
It’s a reality that some recordings will never sound very good, no matter how expensive the gear. In fact the more resolving the gear, the worse such recordings may sound. It seems a waste of time to me to focus gear upgrades on trying to garner improved sonics from such recordings but then, if much of one’s favorite music is poorly recorded/produced, I suppose it’s understandable. Thankfully, I don’t find myself in such a predicament.
Differences I’ve experienced in DACs:
1) Tonality -- some emphasize the upper mids and highs while others are more rolled off and emphasize the lower mids/upper bass. I happen to be very sensitive to highs/forwardness. I’ve played guitar for 50 + years and tonality has always been a top priority in choosing guitars. I don’t like muddy sounding guitars or bright sounding guitars. Same with audio. It’s not easy to build a guitar that is both warm and clear sounding. Many overemphasize upper mids and highs and truncate bass in an effort to improve clarity and so-called "balance". Much current audio gear, to my ears, sounds like it's voiced to sound "lively" or "energic" and to me this typically translates to fatiguing.
2) "Organic" vs. "Clinical" or Natural vs. Analytic: Some DACs I’ve heard have sounded "dry" while others are more ’liquid". I lack the vocabulary to explain this further, except to say that I associate leaner mids and tipped up highs with the clinical sound. Some DACs have behaved more like lab equipment, akin to a microscope. They’ve emphasize resolution above all else, which sounds very unnatural to me. Not my cup of tea.
3) Bass and 4) Soundstaging
There are other categories I’m probably forgetting. The above are the most obvious to me and reflect my particular priorities. As always, YMMV. I’m more of a music lover than an audiophile so there are factors to which I pay little attention that might figure largely in your gear choices.
As @moonwatcher correctly states:
We all have different ears (hearing) and sonic priorities. Some may say natural tone or body of sounds and the attack and decay are most important, others will say soundstage and imaging. Some want it all, if they can get it at a price they are willing to pay. We choose our priorities.